Process for retorting oil shale in the absence of shale ash

ABSTRACT

IN THE PYROLYSIS OF OIL SHALE TO SHALE OIL, THE LOSS OF THE SHALE OIL PRODUCT BY SORPTION ON POROUS SHALE ASH IN THE PYROLYSIS ZONE IS PREVENTED BY ATTRITING THE SHALE ASH PARTICLES TO FINES AND ELUTRIATING THE FINES FROM THE HEAT   CARRIER CIRCUIT SO THAT THE HEAT CARRIERS RECYCLED TO AND USED IN THE PYROLYSIS ZONE ARE SUBSTANTIALLY FREE OF SHALE ASH.

Sept. 12, 1972 J. H. BARNEY ETAL PROCESS FOR RETQRTING OIL SHALE IN THEABSENCE OF SHALE ASH Filed Aprll 1a. 1971 1NVE.\'TORS. BARNEY JOHN H.

FRANKLIN B. CARLSON nited States Patent 3,691,056 PROCESS FOR RETORTINGOIL SHALE IN THE ABSENCE OF SHALE ASH John H. Barney, Denver, andFranklin B. Carlson, Bloomfield, Colo., assignors to The Oil ShaleCorporation,

New York, N.Y.

Filed Apr. 13, 1971, Ser. No. 133,507 Int. Cl. C10b 53/06 U.S. Cl.208-11 5 Claims ABSTRACT OF THE DISCLOSURE In the pyrolysis of oil shaleto shale oil, the loss of the shale oil product by sorption on porousshale ash in the pyrolysis zone is prevented by attriting the shale ashparticles to fines and elutriating the fines from the heat carriercircuit so that the heat carriers recyled to and used in the pyrolysiszone are substantially free of shale ash.

The present invention relates to a process for the recovery of shale oilfrom oil shale which contains substantial amounts ofcarbonate-containing minerals.

BACKGROUND OF THE INVENTION As the worlds petroleum reserves become moredepleted and/or nationalized, increasing attention and interest is beingdirected to the recovery of shale oil from the plentiful reserves of oilshale located in the western states of Colorado and Utah and elsewherethroughout the world.

When oil shale of the type found in the Green River shales of thewestern United States is pyrolyzed at about 800 F. to 1000 F., thekerogen decomposes to gas, oil and spent shale. The oil and gas arerecovered for down stream processing and upgrading. The spent shale is awaste product comprising coke-like residue which contains largequantities of calcite (CaCO and dolomite (MgCO -CaCO having a particlesize as small as /1- inch and smaller. This shale matrix is to bedistinguished from other oil-bearing matrixes such as coal whichcontains minor amounts of ash and tar sands which consist mainly ofdense particles of silica.

Green River shale typically contains carbonate minerals in the range ofabout 35 weight percent dolomite and 15 weight percent calcite. Thespent shale also averages about 3 to 6 weight percent fixed organiccarbon, depending, of course, on the specific pyrolysis processemployed. This amount of fixed carbon in terms of energy constitutesenough heat to sustain a very large retorting facility without resortingto the use of a portion of the oil or gaseous pyrolysis products forsupplying the heat requirement. In this regard, many processes have beenenvisioned which contemplate the use of this available energy source forconducting the pyrolysis reaction, but none of these processes havefully anticipated the gamut of problems inherent in actually recoveringand utilizing this energy source. At least one process (see U.S. Pat.No. 3,281,349) has attempted to cope with a portion of the problem thatarises when spent shale decomposes and produces fines which contaminatethe oil product as base sediment. The solution in this instance wasdirected to avoiding the destruction of the original shape of the rawshale particle by controlling the size of the feed material so as toeasily remove the major portion of the spent shale prior to combustionof carbon deposited on the process heat carrier, i.e., catalyst beads.This procedure also sought to avoid the heat consuming endothermicreaction which occurs as a result of carbonate decomposition when spentshale is combusted. This endothermic reaction is considered therein asundesirable because it consumes heat and produces very fine micron andsub-micron size shale ash particles that contaminate the oil product.

A number of other processes have also described burning the carbon, or aportion thereof from the spent solid residue to furnish hot spentcombustion residue, char, coke or the like, which is recycled to theretort to effect the pyrolysis reaction. Processes of this type, forexample, those disclosed in U.S. Pat. Nos. 2,983,653 and 3,251,751, alsodisclosed adding extraneous heat carriers such as fuel ashes, fireclay,alumina, silica, silicates, catalyst beads, magnesium oxide or likematerials to the heat carrier circuit in conjunction with combustionresidue to maintain an inventory of heat carrier for effecting thepyrolysis reaction. For the most part, the data presented in prior artof this type were derived primarily from tests conducted relative to thedegasification of coal and, then, only broadly relate to the processingof oil shale.

It has now been found that the presence of the combusted spent shaleresidue, i.e., shale ash, in the pyrolysis zone is detrimental to theeconomical recovery of shale oil from oil shale containing substantialamounts of carbonate minerals. This is because the shale ash sorbs asignificant quantity of the product shale oil during the pyrolysisreaction which is subsequently lost to the recovery system. The sorbedoil is burned during the combustion of the spent shale used to providethe heat for reheating extraneous heat-carrying bodies. This sorption isbelieved to be peculiar to oil shales containing substantial carbonatemineral concentrations because upon decomposition of the carbonates, theresidue or shale ash is converted to an extremely fine (50 to weightpercent smaller than 325 mesh or 44 micron), porous and oleophilicmaterial. If this shale ash is allowed to remain in the heat-carriercircuit, the total hydrocarbons available for recovery will be adverselyaffected by sorbing more of the oil product than is necessary to furnishthe overall process heat requirements. As previously noted, the fixedcarbon content of the spent shale alone is generally more thansufiicient to provide the pyrolysis heat requirement. As to theendothermic carbonate decomposition reaction, it has been determinedthat for spent shale combustion tempertaures up to about 1400 F.-theprocess heat requirement is still in balance. Additionally, because ofthe minute particle size of shale ash, substantial levels of basesediment contaminate results from vapor entrainment of this fine ash ifit is not purged from the circuit.

SUMMARY OF THE INVENTION It is therefore, the principal object of thepresent invention to provide a process for the recovery of shale oilfrom oil shale whereby the loss of shale oil by sorption on porous shaleash in the pyrolysis zone is prevented entirely or at leastsubstantially.

In general, the process of the present invention provides for therecovery of shale oil from oil shale via solid-to-solid heat transfertechniques while preventing the loss of shale oil by sorption on porousshale ash in the pyrolysis zone. This is achieved to the process hereindescribed by insuring that the heat-carrying bodies recycled to thepyrolysis zone are free entirely or substantially of shale ash. Theheat-carriers used herein may be any small attrition resistant materialsuch as silica, minute alumina beads, or the like. The shale ash isremoved from the heat carrier body circuit by attrition and elutriationsteps. These steps are preferably carried out in conjunction, however,each step may be performed independently of the other. Thus, incombusting the fixed carbon on the spent shale or shale coke by-productof the pyrolysis of oil shale in a dense phase fluid bed combustion zonecontaining the cooled heat-carrying bodies, the spent shale is convertedto friable particles of shale ash which are attrited to fines byfrictional contact in the turbulent dense phase fluid bed combustionzone and the fines elutriated therefrom by the hot flue gas by-productof combustion. The remainder of the friable shale ash particles areseparated from the reheated heat-carrying bodies by attriting them tofines at a location downstream of the fluid bed combustion zone. This isconveniently accomplished in the present process While transporting theshale ash from the combustion zone to an accumulation zone wherein therecycle heat-carrier is stored prior to being returned to the pyrolysiszone by subjecting the shale ash to a second attrition and elutriationstep. The hot heat-carrying bodies, now free entirely or substantiallyof shale ash, are recycled to the pyrolysis zone to effect the pyrolysisof oil shale to shale oil in the absence of sorbent porous shale ash soas to prevent the loss of shale oil by sorption on the porous shale ashin the pyrolysis zone.

The process further provides for the economical recovery of the heatcontent of the hot flue gas. This heat may be used to preheat raw oilshale fed to the pyrolysis zone if the sorbent shale ash is firstremoved from the gas stream. The heat may be more conveniently recoveredvia indirect heat exchange with the combustion air to the dense phasefluidized bed.

DETAILED DESCRIPTION OF THE INVENTION The process of the invention willbe further illustrated and described in detail in connection with theaccompanying drawing which represents a flow diagram of the process ofthe invention.

Oil shale, previously crushed to a particle size of nominal minus/2-inch, is fed from source 1 to the pyrolysis zone (retort) 2. Theshale may be preheated prior to being fed to the retort by passing thecold shale at about 60 F. through preheater 3. Shale preheating may beaccomplished by recovering the sensible heat from the discharge flue gasproduct of spent shale combustion described below. The sensible heat maybe recovered either directly by entraining the cold shale in a stream ofhot flue gas from which the solid combustion zone products have beenremoved, or indirectly by passing the flue gas through a heat exchangerof the type resembling a bundle of fin tubes. Regardless of the preheatprocedure, it is desirable to preheat the shale to at least 220 F. toremove as much of the free moisture as possible and reduce the size ofthe downstream shale oil recovery equipment.

In one pilot plant test run, the crushed oil shale was preheated toabout 230 F. in a dilute phase fluid bed and fed at an average rate ofabout 1180 pounds per hour into the retort 2 operating at a pressure of0.75 p.s.i.g.

Hot heat-carrying bodies substantially free of shale ash and having anaverage temperature of about 1215 R, which are preferably highlyattrition resistant silica sand particles having the granular particlesize distribution set forth in Table 1 below, are fed from theheat-carrier accumulator 4 to the retort 2 via line 5 at an average rateof about 4000 pounds per hour. The present process contemplates the useof all attrition resistant heat-carrying fluidizable solids having aparticle size range in the order of 100 mesh to about 4.0 mesh.

TABLE 1 Cumulative weight percent In the retort 2, the hot heat-carryingsand particles are mixed with preheated oil shale and conveyedtherethrough. The retention time required in the retort is in the orderof 2 to 5 minutes. The hot sand particles exchange heat with thepreheated oil shale to convert the kerogen content thereof into shaleoil vapors at a temperature of about 950 F. and a spent shale residue.The shale oil vapors comprise noncondensable or gaseous hydrocarbons aswell as vaporized condensable hydrocarbons. The spent shale or shalecoke contains fixed residual carbon in amounts ranging from about 3% toabout 6%.

The typical carbon content of the Green River oil shale found in westernColorado and processed via solidto-solid heat exchange techniques is inthis range. The fixed carbon content of oil shale usually varies withits origin or location and can be as high as 10% or more by weight.Since the fixed carbon represents an available energy source, allefforts should be exerted to recover or utilize it efiiciently.

The solids blend of cooled heat-carrying bodies, i.e., sand, and spentshale particles plus the shale oil vapors pass from the retort 2 into asolids-vapor separator vessel 6. The shale oil vapors collect in theupper portion of the separator 6 and are removed therefrom via conduit 7and passed to a vapor recovery zone or fractionator 8 for furtherdownstream processing.

The solids blend of cooled heat-carrying bodies and spent shaleparticles is withdrawn from the bottom of the separator 6 through thesolids flow control valve 9 via line 10 and passed therethrough to adense phase fluidized bed combustion zone 11 by conventional dense phasetransport procedures. If the solids blend contains a substantialquantity of large spent shale particles, for example, minus one-inch toplus Az-inch size, the particles may be comminuted via crusher 12 priorto entry into the combustion zone 11. Because spent shale is somewhatfriable and easily crushed, the crusher rolls are disposed to imposeonly moderate pressure on the larger spent shale particles withoutfracturing the heat-carriers.

In the fluidized bed combustion zone 11 the carbon content of the solidsblend is combusted to provide the heat for reheating the heat-carryingbodies therein. The heat-carrying bodies are generally covered withdeposited coke, while the spent shale contains coke throughout itsfine-grained matrix. If the fuel requirement provided by the carboncontent of the solids blend fed to the combustion zone 11 isinsufficient to accomplish the desired retorting, additional extraneousfuel may be added to the fluid bed in the form of heavy oil, tar or thelike. The fluidized bed is operated to provide turbulent frictionalcontact within the bed section 13 and freeboard section 14 to therebycause severe attrition of the friable spent shale ash into shale ashfines having a particle size preferable less than 200 mesh. Thefluidized bed is operated at temperatures ranging from about 1100 F. toabout 1650 F. and at fluidizing superficial air velocities of from about2.5 to 6.0 feet per second. The higher combustion temperatures of 1400to 1650 F. are desired because carbonate decomposition of the spentshale more readily occurs, thereby enhancing the breakdown and degree ofattrition of shale ash in the combustion zone. A further product of thecombustion reaction is hot flue gas. The attrited shale ash fines areelutriated from the reheated heatcarrying bodies by the hot flue gas andwithdrawn from the freeboard section 14 via cyclone separator 15 andline 16. The cyclone separator 15 returns any of the largerheat-carrying bodies which may be jetted out of the fluidized bed backto the bed. The hot flue gas which contains shale ash fines is conveyedvia line 25 through a cooler 17 and into a solids removal zone 18, i.e.,bag filter, prior to being discharged to the atmosphere via line 19.

The reheated heat-carrying bodies and any larger remaining particles ofthe friable shale ash not removed with the hot flue gas are withdrawnfrom the dense phase fluid bed combustion zone 11 via standpipe 20. Thereheated heat-carrying bodies and the small remainder of the friableshale ash particles are fed through line 22 by hot air transport gasfrom source 21 into the heat carrier accumulator 4 having therein anelutriator 23 equipped with a plurality of attriter bars or baflles 24.The friable shale ash particles are attrited and comminued by impactingagainst the attriter bars 24 and thereby converted into shale ash fineshaving an average particle size of about 200 mesh (U.S. sieve) orsmaller while the attrition resistant hot heat-carrying bodies are notsignificantly attrited. The elutriator also serves to disperse the shaleash fines so as to significantly improve the elutriation thereof fromthe heat-carrying bodies. The suspension of shale ash fines in the hotair transport gas is withdrawn from the elutriator 23 via line 25 whichjoins line 16 and passes through cooler 17 for cooling prior tosubsequent fines-gas separation and disposal.

The hot heat-carrying bodies, now entirely or substantially free fromshale ash, accumulate in a bed 26 within the base of the heat carrieraccumulator 4. The heat carriers are fed from the accumulator 4 via lineat a temperature of from 1100" F. to 1650 F. into the retort 2 to eifectpyrolysis of fresh oil shale introduced therein. Excess solids arewithdrawn from accumulator 4 via line 27.

In one test conducted over a 16-hour period, the shale ash fines wereallowed to build up in the recycle sand circuit to determine the effectof shale ash fines on the product oil yield. The overall effect wasdetermined by noting the decrease in the fluid bed fuel (natural gas)requirement to maintain an average temperature of about 1400 F. It wasobserved during this test that the whole oil yield decreased as the testprogressed, and that the decrease in oil yield was accompanied by acorresponding decrease in the fluidized bed fuel requirement. The dataare presented in Table 2. Visual inspection of the recycle sand circuitconfirmed that the ash content increased substantially over the testperiod.

TABLE 2.COMPARISON OF OIL YIELD AND FLUID BED FUEL REQUIREMENT NECESSARYTO MAINTAIN 1,400 F. BED TEMPERATURE 1 Weight percent at modifiedFischer assay.

From the foregoing discussion and the data in Table 2 it is evident thatproduct oil was sorbed and burned in the combustion zone. Extraneousfuel was required in all of these pilot plant tests to compensate forheat losses from the small-scale equipment.

In another test conducted to determine the effect of removing the shaleash from the recycle sand circuit on the overall product oil yield, atotal of 8.9 tons "of the same Green River oil shale as used in theabove test were preheated to 230 F. and processed over a test period ofeleven hours. A charge of clean silica sand having the particle sizedistribution set forth in Table 1 above was used for this test. Thefluid bed combustion zone was operated at a superficial air velocity of4.2 feet per second to remove all solids of less than about 200 mesh.Upon completion of the test, it was determined that the recovered oilplus C and heavier gaseous hydrocarbons amounted to 100.5 weight percentof Fischer assay. The total amount of hydrocarbons recovered, which alsoincludes C through C hydrocarbons, oil, and C and heavier gaseoushydrocarbons was 107.2 weight percent of Fischer assay.

From the above description of the process of the invention, it is clearthat it provides for the recovery of shale oil from oil shale withoutthe loss of shale oil by sorption on porous shale ash in the pyrolysiszone and subsequent combustion thereof and loss in the combustion zoneor reheater. This is achieved by insuring that shale ash is not fed intothe pyrolysis zone. Using the process described herein, the shale ashwas removed from the heat carrier circuit by means of a primaryattrition and elutriation step conducted in the dense phase fluid bedcombustion zone and a secondary attrition and elutriation procedureperformed downstream of combustion zone in the heat carrier accumulationzone. By such attrition and elutriation of the shale ash, it is removedfrom the reheated heat carriers so they are fed to the pyrolysis zonefree entirely or substantially of shale ash.

It will be appreciated that various modifications and changes, inaddition to those set forth above, can be made in the process of theinvention by those skilled in the art without departing from the essenceof the invention and that accordingly the invention is to be limitedonly within the scope of the appended claims.

What is claimed is:

1. A process for the recovery of shale oil from oil shale whichcomprises:

(a) pyrolyzing oil shale containing substantial quantities of mineralcarbonates by heating the oil shale with attrition resistant hotheat-carrying bodies substantially free of shale ash in a pyrolysis zoneto form shale oil vapors and a solids blend of cooled heat-carryingbodies and spent shale particles containing fixed carbon;

(b) separating the shale oil vapors from said solids blend in aseparation zone and passing the separated shale oil vapors to a recoveryzone;

(c) attriting the spent shale particles and combusting the carboncontent of the solids blend in a combustion zone to reheat the cooledheat-carrying bodies and to form hot flue gas and fine shale ashparticles;

(d) separating the hot flue gas and fine shale ash particles from thehot heat-carrying bodies to provide hot heat-carrying bodiessubstantially free of shale ash particles; and

(e) recycling the hot heat-carrying bodies substantially free of shaleash to the pyrolysis zone to pyrolyze fresh oil shale fed therein;

whereby loss of shale oil by sorption on porous shale ash in thepyrolysis zone is prevented.

2. The process as defined by claim 1 wherein the heatcarrying bodies areattrition resistant silica sand particles.

3. The process as defined by claim 1 wherein the shale ash fines areseparated from hot heat-carrying bodies by elutriation of the shale ashfines fromthe combustion zone with hot flue gas.

4. The process as defined by claim 1 wherein the spent shale particlesof the solids blend are comminuted prior to entering the combustionzone.

5. A process for the recovery of shale oil from oil shale whichcomprises:

(a) pyrolyzing oil shale by heating the oil shale with hot heat-carryingbodies substantially free of shale ash in a pyrolysis zone to form shaleoil vapors and a solids blend of cooled heat-carrying bodies and spentshale particles containing fixed carbon;

(b) separating the shale oil vapors from said solids blend in aseparation zone and passing the separated shale oil vapors to a recoveryzone;

(c) reheating the cooled heat-carrying bodies in a dense phase fiuid bedcombustion zone by combusting therein the fixed carbon contained in thespent shale particles to form hot flue gas and friable shale ashparticles;

(d) attriting a portion of the friable shale ash particles to fines inthe dense phase fluid bed combustion zone 7 and elutriating therein thefines from the reheated heat-carrying bodies by the hot flue gas;

(e) attriting the remainder of the friable shale ash particles to finesin a heat carrier accumulation zone and elutriating therein the finesfrom the reheated heat-carrying bodies by hot air transport gas toprovide hot heat-carrying bodies free of shale ash; and

(f) recycling the hot heat-carrying bodies free of shale ash to thepyrolysis zone to pyrolyze fresh oil shale fed therein;

whereby loss of shale oil by sorption on porous shale ash in thepyrolysis zone is prevented.

CURTIS R.

References Cited UNITED STATES PATENTS DAVIS, Primary Examiner

